The background to the invention will be described with reference to a particular application. Other applications may occur readily to the reader.
Cellular mobile telecommunications networks utilize electronic apparatus that is mounted outside at base stations. The apparatus includes high power units, for example a radio transmitter that includes a high power wide band amplifier. Being mounted outside the apparatus is subject to whatever weather prevails. Generally, the apparatus is contained by an environmentally sealed outer enclosure that is itself mounted within a ventilated case. It is desired that cooling is normally by natural convection so as to avoid the noise, power consumption and maintenance associated with fans necessary to provide forced convection.